In a motor vehicle equipped with an engine driven power consuming device such as an air-conditioner compressor, it has heretofore been proposed that, under idling condition of the engine, the opening degree of the throttle valve of the carburetor is slightly more increased to feed the engine with a larger amount of air-fuel mixture when such power consuming device starts to run. This is to increase the engine output power to prevent stalling of the engine under such loaded idling condition.
One of the conventional mechanisms materializing the above is a so-called "Fast Idle Control Device (FICD)" which is arranged such that, when the power consuming device begins to run, an intake vacuum of the engine is fed into a vacuum motor, which is mechanically connected to the throttle valve, for slightly increasing the opening degree of the throttle valve.
Apart from this, in the conventional internal combustion engine, it has also been proposed to have a carburetor equipped with a dashpot which functions to prevent the throttle valve from being closed too fast after an acceleration pedal is released for thereby not only effecting smooth deceleration of the engine but also reducing harmful compounds such as hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gases emitted from the engine.
However, in the conventional engine system equipped with the above-mentioned two mechanisms separately, a drawback that the intake section of it becomes bulky and complicated is encountered with the engine system.